GreenTips

There are four basic types of plaster: historic lime plaster, traditional sand cement plaster, gypsum plaster and modern (polymer) modified plaster systems. Gypsum plaster is generally only suitable for internal use

Traditional sand cement systems often use small amounts of additives to improve the workability or performance of the plaster. Modified sand cement systems use significant amounts of man made acrylic polymer technologies to dramatically improve the flexibility and water resistance of the specified systems.

Cement based render systems have a relatively high embodied energy content. The use of sand from a local source and cement with a recycled component will reduce the embodied energy, but care will need to be taken to ensure that the cement selected will not compromise the performance of the render system.

A number of modern floor levelling and finishing systems are solvent based, resulting in the release of VOCs and other potentially dangerous man made chemicals. Such materials should always be used with great care as they can have significant health effects on both installers and building occupants. Emissions from such materials will generally be greatest during the first few weeks after installation. A bake out period is always recommended between installation and occupation of the building to allow internal pollutants to be cleaned out prior to occupation.

Insulated render systems have been the subject of much criticism in recent years due to the high number of New Zealand leaky homes constructed using this system. In most cases the failure of the system was due to either poorly installed flashing and/or using the system for complex details in exposed locations. This weakness is common to all external plaster systems. They always need to be used with care as the most environmentally irresponsible cladding system will always be the one which needs to be replaced after only a few years.

A positive attribute of insulated render systems is their ability to create an excellent unbroken thermal envelope and reduce energy use. If used over a concrete substrate they will also allow the concrete to become an effective thermal mass, therefore stabilising internal temperatures.

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